A skid-steer loader is a compact, highly maneuverable vehicle in which the wheels on opposite sides of the vehicle are independently driven through separate hydrostatic transmissions. Each hydrostatic transmission typically includes a variable displacement hydraulic pump coupled to a hydraulic motor having an output shaft which is connected by a chain and sprocket arrangement to the other wheels on the same side of the vehicle. The pumps are usually mounted in tandem and are driven by a rear-mounted engine. Manual controls are connected to displacement cams on the pumps and maneuvering is accomplished by adjusting the rate and direction of flow output from the pumps through the motor such that the wheels on each side of the vehicle are driven at the desired speeds and in the desired directions to propel and steer the vehicle.
Braking of the vehicle is normally accomplished by placing the controls and their respective pumps in the neutral or null position to interrupt fluid flow to the hydraulic motors. This technique works reasonably well on level ground while the hydrostatic drive systems are operating, however, it does not provide for possible inadvertent contact with the controls which might cause the skid-steer loader to jump out of control. Further, this type of braking generally is not satisfactory during operation over inclined surfaces, and it is not available at all when the hydrostatic drive systems are inoperative or otherwise not functioning properly. There are thus drawbacks to such hydrostatic braking.
For these reasons, skid-steer loaders are usually provided with brake systems which can be locked in engaged position in the manner of parking brakes. There are two basic approaches to such brake systems. One approach has been to provide separate brake assemblies which are individual to each transmission, but which are commonly actuated. This approach, however, is unnecessarily complicated and therefore expensive. In addition, careful adjustment must be maintained to ensure that both brake assemblies are actuated to the same degree at the same time.
Another approach has been to provide a single brake assembly which engages both transmissions. For example, U.S. Pat. No. 4,124,084 discloses a brake system with a common caliper overlying brake discs splined to the motor drive shaft of each hydrostatic transmission. Brake pucks are provided on both sides of each brake disc, and the stack of pucks is actuated by a cam shaft extending transverse to the bore in the caliper containing the pucks. In this system, however, rotational range of the cam shaft between the engaged and released positions is relatively narrow and thus permits only limited adjustment to compensate for wear of the brake pucks. More recently, U.S. Pat. No. 4,480,708 issued to Owatonna Manufacturing Company for an improved brake system incorporating a different actuater arrangement which provides for a wider range of adjustment.
In addition to the problem of effective braking, there is also the problem of effective noise control with hydrostatic transmissions. Skid-steer loaders incorporate dual hydrostatic transmissions, each of which includes a hydraulic drive pump characterized by high pressure, pulsatile operation. A great deal of vibration is thus transferred from the hydraulic drive pumps through the transmissions, which in turn can become quite noisy during operation. The operator sits ahead of the engine and over the transmissions, and thus the vibration and noise can be a significant factor in operating a skid-steer loader. In some cases, this noise factor can be aggravated when a brake system is connected to the hydrostatic transmissions. Both of the brake systems shown in U.S. Pat. Nos. 4,124,084 and 4,480,708 incorporate brake discs splined to driven shafts for limited sliding movement responsive to actuation of the brake pucks. At certain loads and speeds this splined connection can cause severe rattle noise, which is not only distracting and wearisome, but which also sounds like there may be a loose drive chain or another problem developing in the transmissions. Heretofore, there has not been available a practical and economical technique for reducing noise associated with the hydrostatic transmissions and brake systems of skid-steer loaders.